Tex. Business & Commerce Code § 8.402

(a) An issuer may require the following assurance that each necessary indorsement or each instruction is genuine and authorized:

(1) in all cases, a guaranty of the signature of the person making an indorsement or originating an instruction, including, in the case of an instruction, reasonable assurance of identity;

(2) if the indorsement is made or the instruction is originated by an agent, appropriate assurance of actual authority to sign;

(3) if the indorsement is made or the instruction is originated by a fiduciary pursuant to Section 8.107(a)(4) or (5), appropriate evidence of appointment or incumbency;

(4) if there is more than one fiduciary, reasonable assurance that all who are required to sign have done so; and

(5) if the indorsement is made or the instruction is originated by a person not covered by another provision of this subsection, assurance appropriate to the case corresponding as nearly as may be to the provisions of this subsection.

(b) An issuer may elect to require reasonable assurance beyond that specified in this section.

(c) In this section:

(1) "Appropriate evidence of appointment or incumbency" means:

(A) in the case of a fiduciary appointed or qualified by a court, a certificate issued by or under the direction or supervision of the court or an officer thereof and dated within 60 days before the date of presentation for transfer; or

(B) in any other case, a copy of a document showing the appointment or a certificate issued by or on behalf of a person reasonably believed by an issuer to be responsible or, in the absence of that document or certificate, other evidence the issuer reasonably considers appropriate.

(2) "Guaranty of the signature" means a guaranty signed by or on behalf of a person reasonably believed by the issuer to be responsible. An issuer may adopt standards with respect to responsibility if they are not manifestly unreasonable.